Added MIGRATE.md for migrating from Subsonic

This guide describes how to migrate from Subsonic to Libresonic by renaming the database files.

Signed-off-by: Nils Wisiol <info@nils-wisiol.de>

MIGRATE.md

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+Upgrade to Libresonic from Subsonic
+================
+
+This guide helps you to migrate your data from Subsonic to Libresonic. It has been tested with Subsonic 5 to Libresonic 6.
+
+Install Libresonic as described in INSTALL.md. The author of this guide used the standalone solution without Java Tomcat.
+
+After installation of Libresonic, the database needs to be migrated. In preperation for that, stop the Libresonic service
+
+    sudo service libresonic stop
+
+If you ran Subsonic before, your data will be (by default) stored in `/var/subsonic`. Assuming you did not use Libresonic before, we will delete all data from Libresonic
+
+    sudo rm -r /var/libresonic # WARNING: DELETES all Libresonic data (Subsonic data will be kept)
+
+We then copy Subsonic data to Libresonic location. Be aware that a couple of files need to be renamed:
+
+    sudo cp -a /var/subsonic /var/libresonic
+    sudo mv /var/libresonic/subsonic_sh.log libresonic_sh.log
+    sudo mv /var/libresonic/subsonic.log libresonic.log
+    sudo mv /var/libresonic/subsonic.properties libresonic.properties
+    sudo mv /var/libresonic/db/subsonic.backup /var/libresonic/db/libresonic.backup
+    sudo mv /var/libresonic/db/subsonic.data /var/libresonic/db/libresonic.data
+    sudo mv /var/libresonic/db/subsonic.lck /var/libresonic/db/libresonic.lck
+    sudo mv /var/libresonic/db/subsonic.log /var/libresonic/db/libresonic.log
+    sudo mv /var/libresonic/db/subsonic.properties /var/libresonic/db/libresonic.properties
+    sudo mv /var/libresonic/db/subsonic.script /var/libresonic/db/libresonic.script
+  
+Then start Libresonic service again.
+
+    sudo service libresonic start
+
+Your old settings will be there. If you wish, you can delete subsonic data
+
+    sudo rm -r /var/subsonic # Optional, THIS WILL DELETE SUBSONIC DATA
+